For example, in U.S. Pat. No. 460,082, there is disclosed an electric vacuum cleaner which is capable of controlling rotational speed of an electric motor for a suction fan in accordance with an indication of a detected amount of dust under suction wherein an indication of the amount of dust is provided to an operator. However, in the above nmentioned prior art in such a controlling mode, i.e., in an automatic operation mode, it is impossible to temporarily control suction force manually, without regard to the detection signal. Therefore, there is an inconvenience to a user in actual use of the prior art device.
Additionally, in Japanese patent application provisional publication No. 59-14594, an electric vacuum cleaner is disclosed which is capable of controlling suction force by a handle switch provided to a handle of the electric vacuum cleaner having a motor for a suction fan and an AC motor of floor-suction-inlet electric drive. However, the disclosed electric vacuum cleaner has a drawback in that when the handle switch is operated, input power for the motor blower changes gradually, thus, decreasing rotational frequency of the AC motor of the floor-suction-inlet electric drive. Therefore, this fact means that such handle switch operation does not provide an easily sensed response to operation of the handle switch, but gives the operator only a strange feeling.